1. Field of the Invention
The present invention relates, in general, to a method for treating nonbiodegradable wastewater, and in particular, to an oxidation catalyst having various metal activities capable of effectively treating wastewater, a method for preparing the same, a method for recycling the same and a method for treating wastewater using the same.
2. Description of the Prior Art
With advances in the industry, various pollutants are produced and their components become nonbiodegradable and highly-concentrated. So, effective treatment of such pollutants has become a main concern.
Further, an allowed discharge standard for pollutants has become more and more stringent owing to serious environmental pollution. However, most wastewater treatment plants treat waste pollutants only by flocculation treatment and a biological method called an activated-sludge method, and thus, do not satisfy such discharge standards.
Toxic compounds contained in wastewater are nonbiodegradable and so are difficult to biologically decompose. Therefore, most pollutants are discharged in the non-decomposed state, thus aggravating water quality as well as creating diverse problems in biological treatment. Thus, there is an urgent need for development of a process capable of effectively treating such wastewater.
In general, such toxic pollutants are chemically treated with an oxidizing agent or a reducing agent and converted to harmless materials. But most of them are chemically stable and not easily reacted with oxidizing or reducing agents.
With the intention of readily performing oxidation or reduction reactions, the temperature or pressure of reaction conditions is increased and thus the reaction may be carried out under super critical state.
However, high treatment costs are required to meet such conditions, so economic loss occurring.
Of the wide range of pollutants, cyanides which are very poisonous and nonbiodegradable substances, are contained in industrial wastewater. In common methods for treating such cyanides, there is provided an alkaline chlorine method, in which cyanide-containing wastewater is adjusted to pH 11-12 and then treated with chlorine as an oxidizing agent.
But this method is disadvantageous in that there are many difficulties in handling chlorine gas, and chlorine is reacted with other materials in treating wastewater under unsuitable conditions, thus producing additional toxic compounds.
In order to overcome the problems of treatment methods of nonbiodegradable wastewater, methods for performing redox reactions using a catalyst are developed. A representative oxidation treatment is the Zimmermann process treating wastewater in the presence of an oxygen gas at high temperature under high pressure [J. Chem. Eng. 65, 117, (1959)]. Thereafter, there has been much improvement in such techniques. Recently, it was reported that toxic wastewater was treated at 150-250xc2x0 C. under 10-70 atm to become harmless, at Nippon Shokubai Co., LTD and Osaka Gas Co., LTD [Harada Yoshiaki, Shokubai, 35 (5), 289, (1993)].
However, these techniques suffer from the disadvantages of high treatment costs attributed to reaction conditions, such as the high pressure of 50 atm and high temperatures of 100-300xc2x0 C., and expensive equipment capable of withstanding high temperature and high pressure. So, in the treatment of large quantities of wastewater, economic loss arises.
Therefore, a catalytic oxidation process, which can be carried out under the conditions of room temperature and atmospheric pressure, is required. An oxidation method using liquid catalyst, such as Fenton oxidation method, is widely used. But this method has the drawback that, since the used catalyst is made to be precipitated and then removed, large amounts of sludge are generated, thus requiring additional processes for removing the sludge.
Meanwhile, through high strength oxidation treatment methods widely known in recent years, radicals having high oxidability are produced from an oxidizing agent and allow various pollutants in water to be oxidized, in which the useful radical is the OH radical having high oxidability, produced from the decomposition of hydrogen peroxide or ozone. Such method includes H2O2/UV, H2O2/ozone, H2 O2/ozone/UV and so on.
However, the above method suffers from high initial costs and high operation costs, because of additional equipment, such as UV lamps or an ozone generator.
So, there is proposed a method for removing hazardous components through catalytic treatment of ozone oxidation (WO 81/02887). But the treatment rate and durability of the catalyst was not satisfactory. In addition, a treatment method of wastewater using a water-treatment catalyst obtained by using various transition metals to ozone and honeycomb-shaped TiO2xe2x80x94ZrO2 is devised (Korean Pat. Publication No. 94-6404, No. 3685), but the catalyst having the structure limited to a honeycomb shape is unsuitable for use in the treatment of wastewater, since it mainly functions deodorization and sterilization.
Meanwhile, in another method of treating waste water, TiO2 is attached to particles or powders of activated carbon and are used as a UV light catalyst (Application No. 2000-0031391). However, this method is inappropriate for use in treating nonbiodegradable wastewater, because of carrying out merely weak oxidations to the extent of antibiosis and sterilization by adsorbing microorganism or fungi.
As conventional oxidation catalysts, TiO2 or inorganic material have been used, but they have no surface-adsorption. Also, when activated carbon is used as a supporting material, adsorption of activated carbon and oxidation of catalyst are responsible only for deodorization or antibiosis. So, it cannot be applied to oxidation catalyst for wastewater treatment.
Accordingly, an object of the present invention for alleviating the problems as described above is to provide an oxidation catalyst capable of treating wastewater through oxidation reaction without secondary pollution.
It is another object of the present invention to provide a semi-permanent catalyst having the same efficiency as a new catalyst, even though the catalyst is reused through a sintering process.
It is another object of the present invention to provide a catalyst capable of oxidizing various nonbiodegradable and toxic components and decreasing color intensity in wastewater.
It is another object of the present invention to provide an oxidation catalyst having high durability and excellent catalytic action of the surface, by reforming the surface of activated carbon to increase the attachability of metal and impregnating various metals to the surface.
It is another object of the present invention to provide a catalyst which can effectively remove an oxidizing agent, such as hydrogen peroxide or ozone present in the treated water after an oxidation reaction.
It is a further object of the present invention to provide a method for preparing the oxidation catalyst.
It is a still further object of the present invention to provide a method for recycling the oxidation catalyst.
It is a still further object of the present invention to provide a method for treating wastewater using the oxidation catalyst.